Field of the Invention
This invention relates to a heating/cooling system for furnishings, and more specifically, to human contact furnishings including beds, chairs, couches, seats including vehicles seats. A vehicle seat includes seats in motor vehicles such as cars, trucks, busses and the like and also includes airplane seats, train seats, water craft seats, motorcycle seats, bicycle seats and the like.
Background
The function of heat pumps is to remove heat from a heat source or reservoir at low temperature and to reject the heat to a heat sink or reservoir at high temperature. While many thermodynamic effects have been exploited in the development of heat pumps and refrigeration cycles, one of the most popular today is the vapor compression approach. This approach is sometimes called mechanical refrigeration because a mechanical compressor is used in the cycle. Any improvement in efficiency related to compressor performance can have significant benefits in terms of energy savings and thus have significant positive environmental impact.
Vapor compression heat pump cycles generally contain five important components. The first is a mechanical compressor that is used to pressurize a gaseous working fluid. After proceeding through the compressor, the hot pressurized working fluid is condensed in a condenser. The latent heat of vaporization of the working fluid is given up to a high temperature reservoir, often called the sink. The liquefied working fluid is then expanded at substantially constant enthalpy in a thermal expansion valve or orifice. The cooled liquid working fluid is then passed through an evaporator. In the evaporator, the working fluid absorbs its latent heat of vaporization from a low temperature reservoir often called a source. The last element in the vapor compression refrigeration cycle is the working fluid itself.
In conventional vapor compression cycles, the working fluid selection is based on the properties of the fluid and the temperatures of the heat source and sink. The factors in the selection include the specific heat of the working fluid, its latent heat of vaporization, its specific volume, and its safety. The selection of the working fluid affects the coefficient of performance of the cycle. In an electrochemical compressor the electrochemical characteristics of a potential working fluid is important. Fluids can be selected for active or passive participation in the compression system. An active material is driven through the compressor in a reversible redox reaction whereas passive working fluids are moved through the compressor by association with the electroactive species, in most cases H2.
For a refrigeration cycle operating between a lower limit, or source temperature, and an upper limit, or sink temperature, the maximum efficiency of the cycle is limited to the Carnot efficiency. The efficiency of a refrigeration cycle is generally defined by its coefficient of performance, which is the quotient of the heat absorbed from the sink divided by the net work input required by the cycle.
Any improvement in heat pump systems clearly would have substantial value. Electrochemical energy conversion is considered to be inherently better than other systems due to their relatively high exergetic efficiency. In addition, electrochemical systems are considered to be noiseless, modular, and scalable and can provide a long list of other benefits depending on the specific thermal transfer application.
Dry sorption systems based on metal hydrides to provide heating and cooling, metal hydride heating and cooling systems (MHHCS), are known. The coefficient of performance of most single stage MHHCS systems have been below 0.5 through the 1990's. A decade or so later, coefficient of performance as high as 1.5 has been reported. Most recently, coefficient of performance above 2.5 or better has been shown which can be better than conventional vapor compression systems. A major challenge in the development or application of the MHHCS units has been the development and availability of low capacity (dry) hydrogen compressors that can operate efficiently.
A traditional problem with mating electrochemical compressors to metal MHHCS units has been the need to provide dry hydrogen to the metal hydride units. Metal Hydrides are very sensitive to hydrolysis and any amount of moisture in the hydrogen gas will accelerates the aging of these compounds. In addition, the materials used for storing the hydrides are generally made from low alloy steels that are sensitive to aqueous corrosion as well as to hydrogen embrittlement, and the interactions between these two types of damage caused by the presence of moisture is a significant concern.
Electrochemical systems typically require water for proton mobility and therefore provide a humidified hydrogen stream to the electrochemical compressor. Coupling an electrochemical compressor with a drying operation adds complexity and parasitic energy to the system, and increases both the overall cost of the system and operational costs.
Metal hydride heat pumps as well as electrochemical compressors are known devices with unique features and benefits. However, mating the two units for proper operation for appliances is non-trivial. There are numerous, sometimes subtle, often non-obvious elements that must be incorporated into systems to enable long-term, safe operation of an electrochemical compressor driven metal hydride heat pump.
Therefore, there is a need for a low cost system and method to operate a metal hydride heat pump at low humidity levels
Temperature modified air for environmental control of living or working space is typically provided to relatively extensive areas, such as entire buildings, selected offices, or suites of rooms within a building. In the case of vehicles, such as automobiles, the entire vehicle is typically cooled or heated as a unit. There are many situations, however, in which more selective or restrictive air temperature modification is desirable. For example, it is often desirable to provide an individualized climate control for an occupant seat so that substantially instantaneous heating or cooling can be achieved. For example, an automotive vehicle exposed to the summer weather, where the vehicle has been parked in an unshaded area for a long period, can cause the vehicle seat to be very hot and uncomfortable for the occupant for some time after entering and using the vehicle, even with normal air conditioning. Furthermore, even with normal air-conditioning, on a hot day, the occupants back and other pressure points may remain sweaty while seated. In the winter, it is highly desirable to have the ability to warm the seat of the occupant quickly to facilitate the occupant's comfort, especially where the normal vehicle heater is unlikely to warm the vehicle's interior as quickly.
For such reasons, there have been various types of individualized temperature control systems for vehicle seats. Such temperature control systems typically include a distribution system comprising a combination of channels and passages formed in the back and/or seat cushions of the seat. A thermal module thermally conditions the air and delivers the conditioned air to the channels and passages. The conditioned air flows through the channels and passages to cool or heat the space adjacent the surface of the vehicle seat.
There are, however, drawbacks with existing temperature control systems for seats. For example, in particularly adverse conditions, it may take the conditioned air a long period of time to heat noticeably the seat. In addition, while climate control systems that use thermal modules provide many advantages, they are relatively expensive and thus may not be suitable for all applications.
In addition, current systems employ thermoelectric (peltier) systems that use exotic materials. For many years, the main three semiconductors known to have both low thermal conductivity and high power factor were bismuth telluride (Bi2Te3), lead telluride (PbTe), and silicon germanium (SiGe). These materials have very rare elements which make them very expensive compounds.
In addition, current systems employing thermoelectric (peltier) systems exhibit very poor coefficients of performance (COP); typically under 1. This inefficiency is a significant drawback.
As seat heating applications increase to literally millions of units, both the poor performance, and raw material supply issues make addressing this problem a critical issue. Thus, there is a need for an improved temperature control apparatus for a climate control system for seats.